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          <th width="60%" align="center">Chapter 5. 
                The DbEnv Handle
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            <h2 class="title" style="clear: both"><a id="envcreate"></a>DbEnv</h2>
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      <pre class="programlisting">#include &lt;db_cxx.h&gt;

class DbEnv { 
public: 
        DbEnv(u_int32 flags); 
        ~DbEnv();

        DB_ENV *DbEnv::get_DB_ENV(); 
        const DB_ENV *DbEnv::get_const_DB_ENV() const; 
        static DbEnv *DbEnv::get_DbEnv(DB_ENV *dbenv); 
        static const DbEnv *DbEnv::get_const_DbEnv(const DB_ENV *dbenv); 
        ... 
}; </pre>
      <p>
        The <code class="classname">DbEnv</code> object is the handle for a Berkeley DB environment — 
        a collection including support for some or all of caching, locking, logging and transaction subsystems, as well as
        databases and log files. Methods of the <code class="classname">DbEnv</code> handle are used to configure the environment
        as well as to operate on subsystems and databases in the environment.
    </p>
      <p>
        <code class="classname">DbEnv</code> handles are free-threaded if the 
        <a class="link" href="envopen.html#envopen_DB_THREAD">DB_THREAD</a> flag is specified to the
        <a class="xref" href="envopen.html" title="DbEnv::open()">DbEnv::open()</a> method when the environment is opened.
        The <code class="classname">DbEnv</code> handle should not be closed while any other handle
        remains open that is using it as a reference (for example, 
        <a class="link" href="db.html" title="Chapter 2.  The Db Handle">Db</a> or <a class="link" href="txn.html" title="Chapter 13.  The DbTxn Handle">DbTxn</a>). 
        Once either the
        <a class="xref" href="envclose.html" title="DbEnv::close()">DbEnv::close()</a> or 
        <a class="xref" href="envremove.html" title="DbEnv::remove()">DbEnv::remove()</a> 
        methods are called, the handle may not be accessed again, regardless of the method's return.
    </p>
      <p>
        The constructor creates the <code class="classname">DbEnv</code> object. 
        The constructor allocates memory internally; calling the 
        <a class="xref" href="envclose.html" title="DbEnv::close()">DbEnv::close()</a> or 
        <a class="xref" href="envremove.html" title="DbEnv::remove()">DbEnv::remove()</a> 
         methods will free that memory.
    </p>
      <p>
            Before the handle may be used, you must open it using the 
            <a class="xref" href="envopen.html" title="DbEnv::open()">DbEnv::open()</a>
            method.
    </p>
      <p>
            The <span class="bold"><strong>flags</strong></span> parameter must be set to 0.
    </p>
      <div class="itemizedlist">
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          <li>
            <p><a id="env_DB_CXX_NO_EXCEPTIONS"></a>
                        <code class="literal">DB_CXX_NO_EXCEPTIONS</code>
                    </p>
            <p>
                            The Berkeley DB C++ API supports two different error behaviors. By default, whenever an error
                            occurs, an exception is thrown that encapsulates the error information. This
                            generally allows for cleaner logic for transaction processing because a try block can
                            surround a single transaction. However, if
                            <code class="literal">DB_CXX_NO_EXCEPTIONS</code> is specified, exceptions
                            are not thrown; instead, each individual function returns an error code.
                    </p>
          </li>
        </ul>
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      <p>
        Each <code class="classname">DbEnv</code> object has an associated <code class="literal">DB_ENV</code>
        structure, which is used by the underlying implementation of Berkeley DB and its C-language
        API. The <code class="methodname">DbEnv::get_DB_ENV()</code> method returns a pointer to this
        struct. Given a <code class="literal">const DbEnv</code> object,
        <code class="methodname">DbEnv::get_const_DB_ENV()</code> returns a const pointer to the same
        struct.
    </p>
      <p>
        Given a <code class="literal">DB_ENV</code> struct, the <code class="methodname">DbEnv::get_DbEnv()</code>
        method returns the corresponding <code class="classname">DbEnv</code> object,
        if there is one. If the <code class="literal">DB_ENV</code> struct was not associated with a
        <code class="classname">DbEnv</code> (that is, it was not
        returned from a call to <code class="methodname">DbEnv::get_DB_ENV()</code>), then the result of
        <code class="methodname">DbEnv::get_DbEnv()</code> is
        undefined. Given a <code class="literal">const DB_ENV</code> struct,
        <code class="methodname">DbEnv::get_const_Db_Env()</code> returns the associated 
        <code class="literal">const DbEnv</code> object, if there is one.
    </p>
      <p>
        These methods may be useful for Berkeley DB applications including both C and C++ language
        software. It should not be necessary to use these calls in a purely C++ application.
    </p>
      <div class="sect2" lang="en" xml:lang="en">
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              <h3 class="title"><a id="idp6652256"></a>Class</h3>
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        <p>
                     <a class="link" href="env.html" title="Chapter 5.  The DbEnv Handle">DbEnv</a>
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      <div class="sect2" lang="en" xml:lang="en">
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              <h3 class="title"><a id="idp6623920"></a>See Also</h3>
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        <p>
                     <a class="xref" href="env.html#envlist" title="Database Environments and Related Methods">Database Environments and Related Methods</a> 
                </p>
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